Discovery of Early Permian tonalite from the high <i>P</i>/<i>T</i> Triassic Suo Metamorphic Complex, Eastern Yamaguchi Prefecture, SW Japan

Abstract

The Suo Metamorphic Complex is characterized as subduction-related Triassic high P/T type metamorphic rocks occurring in southwest Japan. Recently, we have discovered tonalite mylonite ( Otabara tonalite ) from the Tsuno Group, Suo Metamorphic Complex in the western Chugoku province. LA-ICP-MS zircon U-Pb dating of the Otabara tonalite in its type locality yields the magmatic age of . . Ma (MSWD = . ) and . . Ma (MSWD = . ). Whole-rock chemical compositions from the Otabara tonalite show a volcanic arc signature. LA-ICP-MS detrital zircon U-Pb dating of psammitic schist from the Tsuno Group yields the approximated maximum depositional age of Ma with the single peak cluster at ca. Ma and the conspicuous lack of Precambrian zircons. The depositional age of psammitic schist is younger than the crystallization age of the Otabara tonalite. Possible origins of the Otabara tonalite are considered as ) an autochthonous body and a member of the Suo Metamorphic Complex, or ) an exotic block derived from another geotectonic unit. In the case of the possibility ), the arc-type granitoid in the Southern Maizuru Belt is the potential origin of the Otabara tonalite as they share similar ages and geochemical compositions.